Adobe Photoshop version CS2 and higher have a font preview option that will serious slow down your application if you have over 1,000 fonts installed in the windows fonts folder, simply uncheck this option in the type preferences.
I suggest that you install Xiles NexusFont
FREE font manager to preview the fonts that you might like to use this will allow you to preview the typeface in Bold and Italics.
This way you can have as many fonts that you want installed I have over 5,000 and still have Photoshop running as normal without this little tweak even with a P4 with bags of RAM you will fail.
Its also a good idea to use Microsoft Font Validator
in an attempt to find broken fonts this will give you a report on the glyphs and metrics for each suspicious font that you add tot he GUI, if you have over 1,000 fonts leave this running overnight.MIRRORED HERE
Its also a good idea to save the workspace so that you can enter is again later